Why does the frame range setting behave differently when using multiple scenes in the Video Sequence Editor?
In your first scene you have an animation that plays from frame 50 to 80. Frame 50 is the first frame this scene outputs.

When you use that scene in a scene strip in the VSE, this strip plays that output of the scene, the first frame that the VSE scene strip receives is frame 50 from the first scene. This first frame of the scene strip will show up where the scene strip starts, which may be frame 24 of the new scene.

This would give the same result as if you rendered the first scene to disk then added the file on disk to the VSE.

The frame range in scene two has no connection to the original scene frame range.